57

CHAPTER 2

EXPERIMENTAL

This chapter deals with the main experimental techniques employed will

be briefly discussed.

2.1 MATERIALS

Hexane, dichloromethane, chloroform, ethylacetate, ethanol, methanol,

tetrahydrofuran, acetone, N,N-dimethylformamide and water were purified by the

reported procedure (Perrin and Armarego 1998, Furniss et al 1994). Potassium

hydroxide, sodium hydroxide, potassium carbonate, hydrochloric acid (35%),

sodium nitrate, were purchased from Merck, India. 4-hydroxybenzaldehyde, 4-

hydroxyacetanilide, 2,4-dihydroxybenzaldehyde, 4-methoxyaniline, 4-

ethoxyaniline, 4-nitroaniline, 1-bromobutane potassium iodide, phenol, 2,6-

dibromohexane, acrylic acid, methacrylic acid, diethylamine, triethylamine, N,N-

dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridine (DMAP),

isonicotinic acid, were purchased from Aldrich (Bangalore), India. All other

reagent and chemicals were used as received.

2.2 PURIFICATION OF SOLVENT

2.2.1 Dichloromethane

Dichloromethane (100 mL) was shaken with portion of concentrated

sulphuric acid until the acid layer remains colourless and washed with aqueous

5% sodium carbonate solution then with water. Pre-dried with calcium chloride

and distilled over phosphoruspentoxide. The fraction boiling at 40 ºC was

collected and used (lit.b.p.40 ºC, Perrin and Armarego 1998).

58

2.2.2 Chloroform

Chloroform (500 mL) was shaken several times with half of its volume of

10% aqueous sodium bicarbonate and followed by distilled water; the chloroform

layer was separated, dried over fused calcium chloride for 48 h and distilled under

nitrogen atmosphere. The fraction boiling at 62 ºC was collected and redistilled

with P2O5 to get dry chloroform (lit.b.p.62 ºC, Furniss et al 1994).

2.2.3 Ethylacetate

Ethylacetate (1L) was washed with aqueous 5% sodium carbonate

solution then washed several times with sodium chloride and dried with potassium

carbonate. The fraction boiling at 77 ºC was collected (lit.b.p.77.1 ºC, Perrin and

Armarego 1998).

2.2.4 Ethanol

Rectified spirit (1L) was refluxed with calcium oxide for 6 h, set aside

overnight and distilled. The fraction boiling at 80 ºC was collected (lit.b.p.80 ºC,

Furniss et al 1994).

2.2.5 Methanol

Dried methanol was obtained by distilling the commercial methanol (1L)

which was refluxed over anhydrous calcium oxide. The distilled methanol was

treated with magnesium metal and re-distilled. The fraction boiling at 65 ºC was

collected (lit.b.p.65 ºC, Furniss et al 1994).

2.2.6 Acetone

Acetone (1L) was refluxed with successive quantities of potassium

permanganate until the violet colour persisted. It was then dried with anhydrous

potassium carbonate and distilled. The fraction boiling at 57 ºC was collected

(lit.b.p.57 ºC, Furniss et al 1994).

59

2.2.7 N,N-Dimethylformamide

To a 100 mL of N,N-dimethylformamide, freshly roasted copper sulphate

(20 g) was added and stirred. This was left for 24 h until green colour solution

was obtained and filtered. The filtrate was then distilled under reduced pressure

and the fraction boiling at 75 ºC/12mm Hg, was collected (lit. b.p. 75-76

ºC/12mm Hg, Furrniss et al 1994).

2.2.8 Water

Water (1L) was distilled with 10 g of potassium permanganate and

sodium hydroxide. The distilled water was collected and then redistilled to get

double distilled water (b.p. 100 ºC, Furniss et al 1994).

2.2.9 Tetrahydrofuran

Tetrahydrofuran (500 mL) was pre-dried with fused calcium chloride and

filtered. It was then dried with refluxing sodium wire and fractionally distilled at

65.4 ºC (lit.b.p.65.4 ºC, Perrin and Armarego 1998).

2.2.10 Carbon tetrachloride

Carbon tetrachloride (500 mL) was shaken with concentrated sulphuric

acid (100 mL) until there is no further coloration, then several times with distilled

water, dried over fused calcium chloride and distilled. The fraction boiling at 76

ºC was collected (lit.b.p.76.8 ºC, Perrin and Armarego 1998).

60

2.3 Synthesis of 4-Formylphenylisonicotinate (1)

Figure 2.1 Synthesis of compound 1

4-Formylphenylisonicotinate (1) was synthesized by the following

method: A mixture of isonicotinic acid (10 g, 0.08 mol), 4-hydroxybenzaldehyde

(9.9 g, 0.08 mol), DCC (17.8 g, 0.085 mol), and DMAP (5% w/w) were dissolved

in DCM (200 mL), and the resulting mixture was stirred for 12 h at room

temperature under nitrogen atmosphere. Precipitated byproduct urea was filtered

from the reaction mixture and the filtrate was concentrated by vacuum distillation.

The crude product was purified by repeated (three times) recrystallization from n-

hexane. The product 4-formylphenylisonicotinate (Yield 85%) was obtained as a

white powder.

2.4 Synthesis of 4-Butyloxyacetanilide (2)

Figure 2.2 Synthesis of compound 2

The representative synthetic procedure for the compound 4-

butoxyacetanilide (2) is as follows: A mixture of 4-hydroxyacetanilide (6 g, 0.04

61

mol), anhydrous potassium carbonate (10.8 g, 0.08 mol), 1-bromobutane (5.8 g,

0.045 mol) and pinch of potassium iodide in 200 mL of acetone were stirred at 70

ºC for 48 h. Then the reaction mixture was cooled to room temperature, filtered

washed with excess of acetone. The solvent was removed under vacuum to give

white solid. The solid obtained was dissolved in diethyl ether and washed with

water (3 × 300 mL) to remove unreacted 4-hydroxyacetanilide. The organic layer

was dried over anhydrous sodium sulphate, solvent was removed under vacuum

and recrystallized from n-hexane to get bright-white crystals of 4-

butyloxyacetaniline (Yield 68%).

2.5 Synthesis of 4-Butyloxyaniline (3)

Figure 2.3 Synthesis of compound 3

4-Butyloxyaniline (3) was synthesized by the following method: The

compound 4-butyloxyacetanilide (5 g, 0.024 mol) was dissolved in ethanol (150

mL), 20 mL of concentrated HCl in ethanol (25 mL) was added dropwise to the

reaction mixture. The reaction mixture was heated to reflux for 12 h, cooled and

poured into ice-water mixture. The dark brown liquid obtained was extracted by

diethyl ether and washed with water (3 × 300 mL). The organic layer was dried

over anhydrous sodium sulphate, solvent was removed under vacuum to give dark

brown liquid (Yield 81%).

62

2.6 Synthesis of 4-((4-Alkyloxyphenylimino)methyl)phenylisonicotinate

(4a-4b)

Figure 2.4 Synthesis of compound 4(a)

4-((4-Alkyloxyphenylimino)methyl)phenylisonicotinate (4a-4b) were

synthesised by the following method and as a representative synthetic procedure

for the series, the synthesis of compound 4-((4-methoxyphenylimino)methyl)

phenylisonicotinate (4a) is as follows: To a mixture of 4-formylphenyl

isonicotinate (8 g, 0.057 mol), 4-methoxyaniline (7.1 g, 0.057 mol) were

dissolved in methanol (100 mL) and catalytic amount of glacial acetic acid was

placed into the reaction mixture. The reaction mixture was refluxed with constant

stirring at 70 ºC for 2 h. The resulting product was transferred to crushed ice and

the solid formed was filtered, washed with dilute methanol. Then the crude

product was recrystallized from dichloromethane to get the desired yellow product

(Yield 94%). A similar procedure was adopted for preparation of butyoxy (4b)

compound.

63

2.7 Synthesis of 4-(4-Methoxyphenyliminomethyl)benzene-1,3-diol (5)

Figure 2.5 Synthesis of compound 5

4-(4-Methoxyphenyliminomethyl)benzene-1,3-diol (5) was synthesised

by the following method. To a mixture of 2,4-dihydroxybenzaldehyde (8 g, 0.057

mol), 4-methoxyaniline (7.1 g, 0.057 mol) were dissolved in methanol (100 mL)

and catalytic amount of glacial acetic acid was placed into the reaction mixture.

The reaction mixture was refluxed with constant stirring at 70 ºC for 2 h. The

resulting product was transferred to crushed ice and the solid formed was filtered,

washed with dilute methanol. Then the crude product was recrystallized from

dichloromethane to get the desired yellow product (Yield 94%).

2.8 Synthesis of 1-Bromo-6-(4-methoxyphenylimino-2-hydroxy-4’-

oxy)hexane (6)

Figure 2.6 Synthesis of compound 6

64

1-Bromo-6-(4-methoxyphenylimino-2-hydroxy-4'-oxy)hexane (6) was

synthesized by the following method: The compound 4-(4-methoxyphenyl-

iminomethyl)benzene-1,3-diol (5) (6 g, 0.025 mol), K2CO3, (3.4 g, 0.050 mol) and

catalytic amount of KI were dissolved in 100 mL of acetone. The mixture was

refluxed for 10 minutes then 1,6-dibromohexane (6 g, 0.025 mol) in 20 mL of

acetone was added drop by drop to this reaction mixture while continuously

stirring. The reaction mixture was further refluxed with constant stirring at 70 ºC

for 24 h. The salt formed was filtered, washed with 100 mL of acetone and the

solvent was evaporated under reduced pressure. The crude product was purified

by column chromatography (ethylacetate/hexane (1/9) used as eluent) to get pale

yellow solid (Yield 65%).

2.9 Synthesis of 6-((4-Methoxyphenylimino-2-hydroxy)phenyl-4'-

oxy)hexyl methacrylate (7)

Figure 2.7 Synthesis of compound 7

6-(4-Methoxyphenylimino-2-hydroxyphenyl-4'-oxy)hexyl methacrylate

(7) was synthesized by the following method: Methacrylic acid (0.25 mol) was

added drop by drop to K2CO3 (0.50 mol) and stirred at room temperature for 5

minutes and allowed for the formation of potassium methacrylate. A solution of

1-bromo-6-(4-methoxyphenyl- imino-2-hydroxy-4‟-oxy)hexane (6) (0.25 mol)

and hydroquinone 0.05 gm in N‟N-dimethylformamide (50 mL) was added to the

potassium methacrylate and the resulting mixture was stirred at 90 ºC for 12 h.

65

The reaction mixture was allowed to cool and transferred to distilled water. The

precipitate was collected and dissolved in dichloromethane. The organic layer

was separated and evaporated under reduced pressure. The crude product was

collected and purified by column chromatography (Ethylacetate/hexane (1/9) as

the eluent) to get pale yellow solid (Yield 74%).

2.10 Synthesis of 4-(6-Hydroxyalkyloxy)benzoic acid (8a-8b)

Figure 2.8 Synthesis of compound 8a

4-(6-Hydroxyalkyloxy)benzoic acid (8a-8b) were synthesized by the

following method and as a representative synthetic procedure for the series, the

synthesis of compound 4-(6-hydroxyhexyloxy)benzoic acid (8a) is as follows: To

a mixture of 4-hydroxybenzoic acid (8 g, 0.057 mol), 6-bromohexan-1-ol (10.4 g,

0.06 mol), potassium carbonate (16.4 g, 0.114 mol) and catalytic amount of KI

were dissolved in 100 mL of acetone. The mixture was refluxed with constant

stirring at 70 ºC for 24 h. The salt formed was filtered, washed with 100 mL

acetone and the solvent was evaporated under reduced pressure. The formed crude

product was used for further step reaction (Yield 66%). A similar procedure was

adopted for preparation of octyloxy (8b) compound.

66

2.11 Synthesis of 4-(6-Acryloyloxyalkyloxy)benzoic acid (9a-9b)

Figure 2.9 Synthesis of compound 9a

4-(6-Acryloyloxyalkyloxy)benzoic acid (9a-9b) were synthesized by the

following method and as a representative synthetic procedure for the series, the

synthesis of compound 4-(6-acryloyloxyhexyloxy)benzoic acid (9a) is as follows:

Acrylic acid (0.21 mol) was dissolved in chloroform (150 mL), and then thionyl

chloride (50 mL, 0.62 mol) was added drop by drop to the reaction mixture. The

resultant mixture was refluxed with constant stirring at 80 ºC for 6 h. The

chloroform and excess thionyl chloride were removed under vacuum distillation

to get acid chloride as colourless liquid (Yield 92%) (Petersen 1953). The

acryloyl chloride (0.1 mol) dissolved with 100 mL dry tetrahydrofuran (THF) and

4-(6-hydroxyhexyloxy)benzoic acid (0.1 mol) followed by dry triethylamine (0.12

mol) were added and stirred at 5 to 15 ºC for 12 h under nitrogen atmosphere.

The precipitated triethylamine hydrochloride salt was removed and the product is

dissolved in THF and filtered. The filtrate was removed under vacuum distillation

to get crude product, then recrystallized from ethanol to get white crystals (Yield

90%). A similar procedure was adopted for preparation of octyloxy compound.

67

2.12 Synthesis of 4-Hydroxy-4′-methoxyazobenzene (10a-10b)

Figure 2.10 Synthesis of compound 10a

The representative synthetic procedure for the compound 4-hydrox-4ʹ-

methoxy azobenzene (10a) is as follows: 4-methoxyaniline (6.16 g, 0.05 mol,)

was dissolved in 3 mol/L hydrochloric acid (50 mL). After complete dissolution,

the solution was cooled with an ice-salt mixture to a temperature below 5 °C.

With vigorous stirring, to this cold solution was added slowly a solution of

sodium nitrite (3.5 g, 0.05 mol) in 10 mL of water. The resulting diazonium

solution, kept below 5 °C, was subsequently added drop wise to a cold solution of

phenol (4.7 g, 0.05 mol) in 25 mL of 10% aqueous sodium hydroxide. The dark

brown suspension was acidified, and the precipitate was collected. The crude

product was washed with water and dried under vacuum. The crude product was

washed with CCl4 to get the product (Yield 82%). A similar procedure was

adopted for the preparation of 4-Hydroxy-4′-nitroazobenzene (10b).

68

2.13 Synthesis of 1-Bromo-4-(4-methoxyazobenzene-4′-oxy)alkane

(11a-11d)

Figure 2.11 Synthesis of compound 11a

1-Bromo-4-(4-methoxyazobenzene-4′-oxy)alkane (11a-11d) were

synthesised by the following method and as a representative synthetic procedure

for the series, the synthesis of compound 1-bromo-4-(4-methoxyazobenzene-4′-

oxy)hexane (11a) is as follows: A mixture of 4-hydroxy-4ʹ-methoxyazobenzene

(6.85 g, 0.03 mol), 1,6-dibromohexane (13 g, 0.06 mol), potassium carbonate (4.2

g, 0.03 mol) and acetone were refluxed with constant stirring at 70 ºC for 24 h.

The reaction mixture was filtered at hot condition and the residue was washed

with acetone. The acetone was removed under reduced pressure and petroleum

ether (30-60 °C) was added to the concentrated organic extracts. The resulting

precipitate was collected and dried. The crude product was recrystallized with hot

filtration from ethanol to get desired product (Yield 64%). A similar procedure

was adopted for the preparation of 11b-11d compounds.

69

2.14 Synthesis of Triethylammonium-Functionalized 1-Bromo-4-(4-

methoxyazobenzene-4′-oxy)alkane (12a-12d)

Figure 2.12 Synthesis of compound 12a

Triethylammonium-Functionalized 1-Bromo-4-(4-methoxyazobenzene-

4′-oxy)alkane (12a-12d) were synthesized by following method and as a

representative synthetic procedure for the series, the synthesis of compound

triethylammonium-functionalized 1-bromo-4-(4-methoxyazobenzene-4′-oxy)

hexane (12a) is as follows: 1-bromo-4-(4-methoxy- azobenzene-4′-oxy)hexane

(3.5 g (0.01 mol) was dissolved in 25 mL of absolute ethanol. To the warm

solution, 5 mL of triethylamine in alcohol (10 mL) was added drop by drop and

the resulting mixture was refluxed with constant stirring at 95 ºC for 24 h. Ethanol

was removed by evaporation. The crude product was purified by recrystallization

from ethanol to get yellow crystals (Yield 86%). A similar procedure was

adopted for the preparation of 12b-12d compounds.

70

2.15 Synthesis of poly[4-(6-Acryloyloxyalkyloxy)benzoic acid] (13a-13b)

Figure 2.13 Synthesis of compound 13a

Side-chain polymer was synthesised by free radical polymerization using

AIBN as free radical initiator in THF. Poly[4-(6-acryloyloxyalkyloxy)benzoic

acid (13a-13b) were synthesized by the following method and as a representative

synthetic procedure for the compound poly[4-(6-acryloyloxyhexyloxy)benzoic

acid] (13a) is as follows: 4-(6-acryloyloxyhexyloxy)benzoic acid (9a) (1 g) and

AIBN (2 mol %) were dissolved in dry THF. Then dry nitrogen gas was purged

for 15 minutes. The polymerization tube was closed and kept in oil bath at 60 ºC

for 48 h. The resulting polymer solution was cooled and poured into excess of n-

hexane to precipitate the polymer. The polymer was purified by precipitating

twice using chloroform and n-hexane. The purified polymer was dried under

vacuum at 40 ºC for 48 h. A similar procedure was adopted for preparation of

other polymers such as poly[4-(6-acryloyloxyoctyloxy)benzoic acid] (13b),

poly(acrylic acid) (PAA) (14), poly(methacrylic acid) (PMA) (15) and poly[6-((4-

methoxyphenylimino-2-hydroxy)phenyl-4'-oxy)hexyl methacrylate] (poly

(6M2HM)) (16).

71

2.16 Synthesis of target self-assembled compounds

2.16.1 Synthesis of poly[6-((4-Methoxyphenylimino-2-hydroxy)phenyl-4'-

oxy)hexyl methacrylate]–4-((4-alkyloxyphenylimino)methyl)phenyl

isonicotinate hydrogen bonding complexes (Ia-Ib)

Figure 2.14 Synthesis of compounds Ia-Ib

A typical procedure for the synthesis of Ia-Ib is as follows: To a mixture

of equimolar amount of poly[6-((4-methoxyphenylimino-2-hydroxy)phenyl-4'-

oxy)hexyl methacrylate] (16) and 4-((4-methoxyphenylimino)methyl)phenyl

isonicotinate (4a) in chloroform/THF (1:1 vol) and heated slowly to 50 ºC until

complete solubilisation of compounds. The solvent was evaporated slowly under

atmospheric pressure. The obtained powder complex (Ia) was dried under

vacuum at 40 ºC for 3 days. The above synthetic procedure was adopted for the

preparation of Ib complex.

72

2.16.2 Synthesis of poly[4-(6-acryloyloxyalkyloxy)benzoic acid]– 4-((4-

alkyloxyphenylimino)methyl)phenylisonicotinate hydrogen

bonding complexes (IIa-IId)

Figure 2.15 Synthesis of compounds IIa-IId

A typical procedure for the synthesis of IIa-IId is as follows: To a

mixture of equimolar amount of poly[4-(6-acryloyloxyhexyloxy)benzoic acid]

(13a) and 4-((4-methoxyphenylimino)methyl)phenylisonicotinate (4a) in

chloroform/THF (1:1 vol) and heated slowly to 50 ºC until complete solubilisation

of compounds. The solvent was evaporated slowly under atmospheric pressure.

The obtained powder complex (IIa) was dried under vacuum at 40 ºC for 3 days.

The above synthetic procedure was adopted for the preparation of other (IIb, IIc,

and IId) complexes.

73

2.16.3 Synthesis of poly(acrylic/methacrylic acid) – 4-((4-alkyloxy

phenylimino)methyl)phenylisonicotinate hydrogen bonding

complexes (IIIa-IIId)

Figure 2.16 Synthesis of compounds IIIa-IIId

A typical procedure for the synthesis of IIIa-IIId is as follows: To a

mixture of equimolar amount of poly(acrylic acid) (14) and 4-((4-

methoxyphenylimino)methyl)phenylisonicotinate (4a) in chloroform/THF (1:1

vol) and heated slowly to 50 ºC until complete solubilisation of compounds. The

solvent was evaporated slowly under atmospheric pressure. The obtained powder

complex (IIIa) was dried under vacuum at 40 ºC for 3 days. The above synthetic

procedure was adopted for the preparation of other (IIIb-IIId) complexes.

74

2.16.4 Synthesis of poly(methacrylic acid) – Triethylammonium-Functio-

nalized 1-bromo-4-(4-ethoxyazobenzene-4′-oxy)alkane Ionic self-

assembled complexes (IVa-IVd)

Figure 2.17 Synthesis of compounds IVa-IVd

A typical procedure for the synthesis of ionic self-assembled complexes

(IVa-IVd) is as follows: To a mixture of 10 mg/mL of poly(methacrylic acid)

(15) in double distilled water was added drop wise to triethylammonium-

functionalized 1-bromo-4-(4-ethoxyazobenzene-4′-oxy)hexane (12a) aqueous

solution with concentration of 3 mg/mL, in 1:1 molar ratio. The precipitated

complex (IVa) was washed with several times with double distilled water to

remove residual salts and possible noncomplexed precursors and then dried under

vacuum at 50 ºC for 3 days. The above synthetic procedure was adopted for the

preparation of other (IVb-IVd) complexes.

2.17 CHARACTERIZATION OF COMPOUNDS

In our studies, a combination of different experimental techniques has

been used to characterize the structural and phase behaviour of liquid crystalline

materials. They include direct space techniques such as FTIR and NMR

spectroscopy to ascertain the chemical structure, polarized optical microscopy

(POM) for identification of mesophase, X-ray diffraction analysis for

75

conformation of mesophase, thermogravimetric analysis and differential scanning

calorimetry (DSC) were employed to study the thermal stability and thermal

transition temperature occurring liquid crystalline system, gel-permeation

chromatography and viscosity measurements were studied for molecular weight

determination of polymers.

2.17.1 Viscosity

1% solutions of the polymer in N,N'-dimethylformamide (DMF) were

prepared and filtered through glass filter to remove dust particles. The dust free

polymer samples were taken in an Ubbelohde suspended level viscometer with a

flow time of 160 seconds for DMF at room temperature. Flow times for the

polymer solution and solvent were recorded at the same temperature. Intrinsic

viscosities [η] for the polymer solutions were determined using the following set

of expressions.

Relative viscosity ηr = t2/t1

Where t1 and t2 are time of flow for solvent and polymer solution respectively.

Specific viscosity ηsp = ηr = 1

The intrinsic viscosity [η] was calculated by plotting ηsp/C versus C and extra

plotting the straight line to zero concentration.

2.17.2 Gel permeation chromatography

The weight average molecular weight (Mw) and number average

molecular weight (Mn) of the polymers were determined by Waters 1515

separation module using polystyrene as a standard and THF as an eluent.

2.17.3 Elemental analysis

Elemental analysis was carried out on a Heraeus-CHNO rapid

elemental analyser with sample weight 2 mg.

2.17.4 Fourier Transform Infrared Spectroscopy

Fourier Transform Infrared Spectroscopy (FT-IR) is multidisciplinary

analytical tool yields information pertaining to the structural details of a chemical

76

compounds. FT-IR involves the absorption of electromagnetic radiation in the

infrared region of the spectrum which results change in the vibrational energy of a

molecule. It is a valuable and formidable tool in identifying organic compounds

has polar chemical bonds such as –OH, –NH, –CH, etc., with good charge

separation. Since every functional group has unique vibrational energy, the IR

spectra can be seen as their fingerprint region. FT-IR spectrometer (Shimadzu

FTIR 8300/8700) was used to substantiate the formation of products in this study.

The spectra recorded for solid samples were made into a thin film using

transparent KBr (Merck, IR Grade) pellets. About 10 mg of the samples was grind

with about 70 mg of spectral grade KBr to form a mixture, which was then made

into a pellet using a hydraulic pressure. All the spectra were recorded in the range

of 4000 to 400 cm-1

at a resolution of 4 cm-1

with a maximum of 100 scans. A

background spectrum was run before recording the spectra for each sample. The

spectral calibration of the instrument was made using a KBr film at regular

intervals of time.

2.17.5 Nuclear Magnetic Resonance Spectroscopy

Nuclear magnetic resonance spectroscopy (NMR) is a spectroscopic

method is even more important to the organic chemist than infrared spectroscopy.

Many nuclei may be studied by NMR techniques, but hydrogen and carbon are

most commonly investigated. Whereas infrared spectroscopy reveals the types of

functional groups present in a molecule, NMR gives information about the

number of magnetically distinct atoms of the type being studied.

High-resolution 1H-NMR and

13C-NMR spectra were recorded using

Brucker EX-400 FT-NMR spectrometer. Deuterated chloroform [Aldrich, CDCl3,

99.8% containing 0.03% V/V tetramethylsilane (TMS)] and DMSO-d6 were used

as solvents for recording NMR spectra. The proton NMR were recorded using

broadband inverse probe where the inner coil for the protons and outer coil for „X‟

nuclei. Solvent suppression was applied in some cases where the solvent signal is

very strong compared to the sample signals.

77

2.17.6 Differential Scanning Calorimetry

Differential canning calorimetry (DSC) has become a method of choice

for quantitative studies of thermal transition in polymers. Differential scanning

calorimetry was performed using the Universal V4.5A DSC Instrument DSC Q20

V24.2 Build-107 calorimeter and Mettler Toledo STAR system thermal analysis

unit attached to a DSC module. The experiments were carried out in nitrogen

atmosphere at a heating rate of 5 ºC/min from room temperature to ambient 500

ºC with nitrogen flow of 10 mL/min.

Generally, DSC measures the power released or absorbed by materials

during temperature treatments that can include dynamic (i.e., heating or cooling

ramps) or isothermal segments. The measurement is performed by comparing the

temperature of the sample and that of the reference materials. The instantaneous

heat flux is computed from this temperature difference using instrumental

calibration constant. Standard samples like pure indium or zinc with known

transition enthalpies and temperatures are used for the calibration.

The measuring cell of a calorimeter includes the sample and reference

material enclosed in a single furnace. The DSC furnace is made of silver and

separated from the DSC sensor by a ceramic plate. The temperature of each of the

two containers (pans) is measured by thermocouples connected in series and

located around each of them.

The measuring of enthalpy variation can allow assigning a given

thermal event to a polymorphic crystal to crystal or to a mesophase to mesophase

transition in LC systems. This is based on the fact that the enthalpy variation

associated with crystal melting by far more important than the one corresponding

to the mesophase to mesophase or mesophase to isotropic transitions.

The DSC is a convenient tool to measure the temperatures and

transition enthalpies to determine the phase diagram of the each self-assembled

complexes and to study the kinetics of transition as a function of heating/cooling

rates or as a function of time. DSC has become a method of choice for

78

quantitative studies of thermal transition in polymer and its self-assembled

complexes.

2.17.7 Polarizing Optical Microscope

Polarizing optical microscope (POM) was carried out to find out the LC

texture analysis and also determine the phase transition with sensitivity of ± 0.1

ºC. POM studies were performed with a Euromex polarizing microscope attached

with a Linkem HFS 91 heating stage and a TP-93 temperature programmer.

Samples were placed in between two thin glass cover slips and melted with

heating and cooling at the rate of 2 ºC/min. The photographs were taken from

Nikon FM10 camera. All the micrographs were taken from the second cooling

stage from isotropic transition temperature.

2.17.8 X-Ray Diffraction Measurement

X-ray diffraction measurements were carried out to investigate the

texture of the mesophase. Powder samples were used to obtain diffraction

patterns of liquid crystalline compounds. The powder samples held in sealed

capillaries were heated from room temperature to mesophase and irradiated. The

X-ray was generated by 800 W Philips (PANANALYTICAL, Netherland) powder

diffractometer using anode diffractometer with Cu-Kα radiation. Samples placed

on a mettle FP 52 hot stage.

2.17.9 Thermogravimetric analysis

Thermal degradation of polymer and its self-assembled complexes were

determined by Universal V4.5A TA Instrument SDT Q600 V24.2 Build-107

thermogravimetric analyser. All the TGA data were measured under a nitrogen

atmosphere at a heating rate 10 ºC/min, and the thermal degradation temperature

was determined at the point of 95 wt% of the original weight.

2.17.10 Ultraviolet-Visible (UV-vis) Spectroscopy

UV-visible spectra were obtained at Hewlett-Packard 8435 UV-visible

spectrophotometer. Samples were prepared in the form of solution or thin films.